In the field of programmable logic controllers (PLCs), communication between a PLC and other devices, such as external devices, is typically accomplished by electro-mechanical means through a backplane or fixed connector on the PLC. For example, PLCs have traditionally been programmed by transmission of information through a cable that is attached to a program port on the body of the PLC. Such attachment can be cumbersome, unreliable, and relatively costly.
The prior art has in some instances used modems to control, monitor and test/debug PLCs from remote locations. The modem devices are also typically connected to a PLC through the backplane or a fixed connector on the PLC.
Radio frequency identification (“RFID”) technology has been used in various fields as a means of identifying articles. RFID technology has been used for identifying parcels, luggage, and other materials. An RFID system generally consists of an antenna; a transmitter/receiver and; a transponder (called an RF chip set or tag) that is electronically programmed with unique identification information. The antenna emits radio signals that activate the RFID tag and write and read data to and from the RFID tag. For example, an antenna mounted on a toll booth may monitor various aspects of traffic by sending RF signals to an RF tag mounted within each passing automobile.
RFID tags are available in many different sizes/shapes and are generally characterized as either passive or active. Active tags are internally powered and are typically readable and writable. Active tags have relatively large amounts of memory. Passive tags operate without an internal power source. Passive tags obtain operating power generated from the reader. Passive tags are typically read-only. RFID systems provide for wireless communication through many materials. RFID tags can also be read at high speeds.
In one example, RFID technology is implemented through an integrated chip set with a PROM for programming an identification (ID) code. The RFID chip set is placed on an article and the ID code may be transmitted to, and stored in, the RFID chip. The ID code is then scanned by a transmitter/receiver. The RFID chip is passive and employs the power of the transmitting signal to energize the RFID coil and to return a signal including the ID code or a signal affirming the ID code.
The use of RFID technology has been limited essentially to identification applications and has not been implemented as a means for transferring data in machines, such as PLCs. It would also be advantageous to have the wireless RFID interface as an integral part of the PLC eliminating the need for communication through the backplane and cables.